Last month, the U.S. Supreme Court ruled that inmates on death row can challenge lethal injection by claiming that the chemicals used are too painful and, therefore, amount to cruel and unusual punishment in violation of the Constitution.

The federal government and most states that have the death penalty use a combination of three drugs to carry out lethal injections: thiopental as a sedative; pancuronium bromide to stop breathing; and potassium chloride to stop the heart.

Around the country, individual doctors have refused to participate in state executions, causing delays and confusion. Earlier this year, the execution of convicted killer and rapist Michael Morales was delayed in California when two court-appointed anesthesiologists refused to take part. In Missouri, no anesthesiologists are answering the state's call to participate in lethal injections since a federal judge ordered the state to have a board-certified anesthesiologist assist in the process.

Many medical groups condemn most forms of participation in the execution process. Read below to see some of these organizations' positions.

American Society of Anesthesiologists (ASA)

Doctors should not help put inmates to death by lethal injection, the president of the ASA wrote in a message to colleagues last month. "The legal system has painted itself into a corner and it is not our obligation to get it out," Dr. Orin F. Guidry wrote on the organization's website. Guidry told AP that he posted the statement in response to a federal judge's order last week halting executions in Missouri until the state takes certain actions, such as finding board-certified anesthesiologists to oversee lethal injections.

Although the group does not have an official policy on the issue, the ASA recognizes the American Medical Association's ethical principles about physician participation in lethal injections, in particular that physicians should not participate in executions.

The AMA's ethics council has guidelines stating that it is unethical for physicians to engage in most aspects of lethal injection because a physician is "dedicated to preserving life." For example, physicians may not select fatal injection sites or start intravenous lines, prescribe or administer drugs used in the process, or consult with or supervise lethal injection personnel. Some actions, such as evaluating a prisoner psychiatrically to determine if the execution can proceed, are approved.

"Do we adhere to the patient's wishes if there's hope of prolonging life or preserving health, or do we simply participate in an execution?... and our position is that's not what doctors are supposed to do; we are healers, we are not killers," Dr. Priscilla Ray of the American Medical Association's ethics council told NPR in February 2006.

Although the AMA is against doctors participating in most aspects of lethal injection, an anonymous survey of medical doctors found that many thought it was acceptable for physicians to participate in various areas of the process.

Some 80 percent of the 482 physicians surveyed in a 2000 study indicated that at least one of the eight actions not permitted by the AMA was acceptable. More than half indicated that five or more of those actions were acceptable, and 34 percent approved all disallowed actions. The full study is available from the Archives of Internal Medicine.

Some physicians, such as Doctor Carlo Musso, a Georgia physician who has participated in several executions, believe that their involvement in capital punishment allows for a more humane death for convicts. Read more from doctors on why they participate in executions in an article by Dr. Atul Gawande "When Law and Ethics Collide - Why Physicians Participate in Executions."

American Nurses Association (ANA)

The ANA says it is strongly opposed to nurse involvement in capital punishment. In its position statement, the association states that "participation in executions is considered contrary to the fundamental goals and ethical traditions of the profession." It cites "The Code for Nurses", nursing's ethical code of conduct, which stipulates that "the nurse does not act deliberately to terminate the life of any person." The ANA goes on to say that the nurses' obligation to refrain from causing death should not be breached, even when sanctioned by the law.